/*
 * Copyright 2014 Open Networking Laboratory
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.onlab.onos.net.statistic.impl;

import com.google.common.base.MoreObjects;
import com.google.common.base.Predicate;
import com.google.common.collect.FluentIterable;
import com.google.common.collect.ImmutableSet;
import org.apache.felix.scr.annotations.Activate;
import org.apache.felix.scr.annotations.Component;
import org.apache.felix.scr.annotations.Deactivate;
import org.apache.felix.scr.annotations.Reference;
import org.apache.felix.scr.annotations.ReferenceCardinality;
import org.apache.felix.scr.annotations.Service;
import org.onlab.onos.core.ApplicationId;
import org.onlab.onos.core.GroupId;
import org.onlab.onos.net.ConnectPoint;
import org.onlab.onos.net.Link;
import org.onlab.onos.net.Path;

import org.onlab.onos.net.flow.FlowEntry;
import org.onlab.onos.net.flow.FlowRule;
import org.onlab.onos.net.flow.FlowRuleEvent;
import org.onlab.onos.net.flow.FlowRuleListener;
import org.onlab.onos.net.flow.FlowRuleService;
import org.onlab.onos.net.statistic.DefaultLoad;
import org.onlab.onos.net.statistic.Load;
import org.onlab.onos.net.statistic.StatisticService;
import org.onlab.onos.net.statistic.StatisticStore;
import org.slf4j.Logger;

import java.util.Collections;
import java.util.Objects;
import java.util.Optional;
import java.util.Set;

import static com.google.common.base.Preconditions.checkNotNull;
import static org.slf4j.LoggerFactory.getLogger;

/**
 * Provides an implementation of the Statistic Service.
 */
@Component(immediate = true)
@Service
public class StatisticManager implements StatisticService {

    private final Logger log = getLogger(getClass());

    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
    protected FlowRuleService flowRuleService;

    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
    protected StatisticStore statisticStore;


    private final InternalFlowRuleListener listener = new InternalFlowRuleListener();

    @Activate
    public void activate() {
        flowRuleService.addListener(listener);
        log.info("Started");

    }

    @Deactivate
    public void deactivate() {
        flowRuleService.removeListener(listener);
        log.info("Stopped");
    }

    @Override
    public Load load(Link link) {
       return load(link.src());
    }

    @Override
    public Load load(Link link, ApplicationId appId, Optional<GroupId> groupId) {
        Statistics stats = getStatistics(link.src());
        if (!stats.isValid()) {
            return new DefaultLoad();
        }

        ImmutableSet<FlowEntry> current = FluentIterable.from(stats.current())
                .filter(hasApplicationId(appId))
                .filter(hasGroupId(groupId))
                .toSet();
        ImmutableSet<FlowEntry> previous = FluentIterable.from(stats.previous())
                .filter(hasApplicationId(appId))
                .filter(hasGroupId(groupId))
                .toSet();

        return new DefaultLoad(aggregate(current), aggregate(previous));
    }

    @Override
    public Load load(ConnectPoint connectPoint) {
        return loadInternal(connectPoint);
    }

    @Override
    public Link max(Path path) {
        if (path.links().isEmpty()) {
            return null;
        }
        Load maxLoad = new DefaultLoad();
        Link maxLink = null;
        for (Link link : path.links()) {
            Load load = loadInternal(link.src());
            if (load.rate() > maxLoad.rate()) {
                maxLoad = load;
                maxLink = link;
            }
        }
        return maxLink;
    }

    @Override
    public Link min(Path path) {
        if (path.links().isEmpty()) {
            return null;
        }
        Load minLoad = new DefaultLoad();
        Link minLink = null;
        for (Link link : path.links()) {
            Load load = loadInternal(link.src());
            if (load.rate() < minLoad.rate()) {
                minLoad = load;
                minLink = link;
            }
        }
        return minLink;
    }

    @Override
    public FlowRule highestHitter(ConnectPoint connectPoint) {
        Set<FlowEntry> hitters = statisticStore.getCurrentStatistic(connectPoint);
        if (hitters.isEmpty()) {
            return null;
        }

        FlowEntry max = hitters.iterator().next();
        for (FlowEntry entry : hitters) {
            if (entry.bytes() > max.bytes()) {
                max = entry;
            }
        }
        return max;
    }

    private Load loadInternal(ConnectPoint connectPoint) {
        Statistics stats = getStatistics(connectPoint);
        if (!stats.isValid()) {
            return new DefaultLoad();
        }

        return new DefaultLoad(aggregate(stats.current), aggregate(stats.previous));
    }

    /**
     * Returns statistics of the specified port.
     *
     * @param connectPoint port to query
     * @return statistics
     */
    private Statistics getStatistics(ConnectPoint connectPoint) {
        Set<FlowEntry> current;
        Set<FlowEntry> previous;
        synchronized (statisticStore) {
            current = getCurrentStatistic(connectPoint);
            previous = getPreviousStatistic(connectPoint);
        }

        return new Statistics(current, previous);
    }

    /**
     * Returns the current statistic of the specified port.

     * @param connectPoint port to query
     * @return set of flow entries
     */
    private Set<FlowEntry> getCurrentStatistic(ConnectPoint connectPoint) {
        Set<FlowEntry> stats = statisticStore.getCurrentStatistic(connectPoint);
        if (stats == null) {
            return Collections.emptySet();
        } else {
            return stats;
        }
    }

    /**
     * Returns the previous statistic of the specified port.
     *
     * @param connectPoint port to query
     * @return set of flow entries
     */
    private Set<FlowEntry> getPreviousStatistic(ConnectPoint connectPoint) {
        Set<FlowEntry> stats = statisticStore.getPreviousStatistic(connectPoint);
        if (stats == null) {
            return Collections.emptySet();
        } else {
            return stats;
        }
    }

    // TODO: make aggregation function generic by passing a function
    // (applying Java 8 Stream API?)
    /**
     * Aggregates a set of values.
     * @param values the values to aggregate
     * @return a long value
     */
    private long aggregate(Set<FlowEntry> values) {
        long sum = 0;
        for (FlowEntry f : values) {
            sum += f.bytes();
        }
        return sum;
    }

    /**
     * Internal flow rule event listener.
     */
    private class InternalFlowRuleListener implements FlowRuleListener {

        @Override
        public void event(FlowRuleEvent event) {
            FlowRule rule = event.subject();
            switch (event.type()) {
                case RULE_ADDED:
                case RULE_UPDATED:
                    if (rule instanceof FlowEntry) {
                        statisticStore.addOrUpdateStatistic((FlowEntry) rule);
                    }
                    break;
                case RULE_ADD_REQUESTED:
                    statisticStore.prepareForStatistics(rule);
                    break;
                case RULE_REMOVE_REQUESTED:
                    statisticStore.removeFromStatistics(rule);
                    break;
                case RULE_REMOVED:
                    break;
                default:
                    log.warn("Unknown flow rule event {}", event);
            }
        }
    }

    /**
     * Internal data class holding two set of flow entries.
     */
    private static class Statistics {
        private final ImmutableSet<FlowEntry> current;
        private final ImmutableSet<FlowEntry> previous;

        public Statistics(Set<FlowEntry> current, Set<FlowEntry> previous) {
            this.current = ImmutableSet.copyOf(checkNotNull(current));
            this.previous = ImmutableSet.copyOf(checkNotNull(previous));
        }

        /**
         * Returns flow entries as the current value.
         *
         * @return flow entries as the current value
         */
        public ImmutableSet<FlowEntry> current() {
            return current;
        }

        /**
         * Returns flow entries as the previous value.
         *
         * @return flow entries as the previous value
         */
        public ImmutableSet<FlowEntry> previous() {
            return previous;
        }

        /**
         * Validates values are not empty.
         *
         * @return false if either of the sets is empty. Otherwise, true.
         */
        public boolean isValid() {
            return !(current.isEmpty() || previous.isEmpty());
        }

        @Override
        public int hashCode() {
            return Objects.hash(current, previous);
        }

        @Override
        public boolean equals(Object obj) {
            if (this == obj) {
                return true;
            }
            if (!(obj instanceof Statistics)) {
                return false;
            }
            final Statistics other = (Statistics) obj;
            return Objects.equals(this.current, other.current) && Objects.equals(this.previous, other.previous);
        }

        @Override
        public String toString() {
            return MoreObjects.toStringHelper(this)
                    .add("current", current)
                    .add("previous", previous)
                    .toString();
        }
    }

    /**
     * Creates a predicate that checks the application ID of a flow entry is the same as
     * the specified application ID.
     *
     * @param appId application ID to be checked
     * @return predicate
     */
    private static Predicate<FlowEntry> hasApplicationId(ApplicationId appId) {
        return new Predicate<FlowEntry>() {
            @Override
            public boolean apply(FlowEntry flowEntry) {
                return flowEntry.appId() == appId.id();
            }
        };
    }

    /**
     * Create a predicate that checks the group ID of a flow entry is the same as
     * the specified group ID.
     *
     * @param groupId group ID to be checked
     * @return predicate
     */
    private static Predicate<FlowEntry> hasGroupId(Optional<GroupId> groupId) {
        return new Predicate<FlowEntry>() {
            @Override
            public boolean apply(FlowEntry flowEntry) {
                if (!groupId.isPresent()) {
                    return false;
                }
                // FIXME: The left hand type and right hand type don't match
                // FlowEntry.groupId() still returns a short value, not int.
                return flowEntry.groupId().equals(groupId.get());
            }
        };
    }
}